If the book is important, then Tome Warlock (Celestial or Hexblade) or Wizard. For a tough wizard, Fighter 1/Wizard X, maybe dare for two starting Fighter levels if Action Surge is something you're interested in. The crossbow would be mostly for show - her true power would be in her spells and her book.

Scrolled through quickly and saw this paragraph and thought "Hah! One of my players is....WAIT A DAMN MINUTE!"